Manufacture of hydrogen peroxide



July 18, J. B MERCE, JR

MANUFACTURE OF HYDROGEN PEROXIDE Filed May 16, 1928 ATTORN EY Patented July 18, 1933 UITED STATES PATENT OFFICE JAMES B. PIERCE, JR., OF CHARLESTON, WEST VIRGINIA1 ASSIGNOR T0 BARIUM REDUCTION CORPORATION, A CORPORATION GF DELAWARE MANUFACTURE OF HYDROGEN PEROXIDE Application led May 16, 1928.

This invention relates to the manufacture of hydrogen peroxide and has for its object certain improvements in the method of manufacturing hydrogen peroxide. The inven- 5 tion also contemplates the recovery and use of certain valuable by-products in the manufacture of hydrogen peroxide.

Various processes are employed in the making of hydrogen peroxide. The great difficulty confronting manufacturers of hydrogen peroxide is that of obtaining a product of uniform and high purity, not to mention the question of cost. In the heretofore customary practice, a final product of high purity is not readily obtained. Certain impurities persist in accompanying the product in its conversion from the raw starting material to the finished product. Moreover, these impurities can only be removed with 2U considerable eort, if at all, and by costly procedures. The materials going into the process are utilized but once, and fresh materials must be employed to continue the process. There is, therefore, a marked need 5 for an improved method of manufacturing hydrogen peroxide.

Accordmg to my invention it is possible to manufacture hydrogen peroxide of high purity. The invention, moreover, contemplates certain economies, such as the recovery in marketable form of valuable by-products, the regeneration of certain of the reagents employed, etc., which makes it possible to combine purity of product With economy of manufacture. rlhe process may be made substantially cyclic.

In accordance with the practice of my invention hydrogen peroxide may be manufactured by subjecting an appropriate metallic compound carrier of oxygen to the action of a suitable acid. A Water soluble salt of that acid is also formed which may be suitably treated to re enerate the acid and to renew the carrier o oxygen, both of which may be re-employed in the further manufacture of hydrogen peroxide.

The principles of my invention will be better understood by considering in some detail the practice of the same during the successive steps leading from the raw starting materials Serial No. 278,354.

to the finished product. In my present preferred practice of the invention, I employ the mineral celcstite (native strontium sulfate, SISO.) as the raw starting material. The celestite is preferably crushed and pulverized to a suitable particle size. rIhe finely divided particles of celestite are then subjected to a tabling, jigging or flotation operation in order to secure a concentrate of strontium sulfate as free as possible from gangue constituents.

T he celestite concentrates are charged into a. suitable receptacle to which is added a concentrated solution of soda ash (NaZCOS) The soda ash liquor contains about 25% sodium carbonate in solution. The pulp mixture of strontium sulfate particles and sodium carbonate liquor is heated and brought to its boiling point. As a result of the reaction, strontium carbonate and sodium sulfate are formed:

(l) SrSO4+ Na2CO3= SrCO3 +Na2SO4 The speed and thoroughness of the reaction are materially aided by the finely divided particle size of the celestite. Due to the enormous surface area offered by the great number of minute particles the soium carbonate liquor can attack the strontium sulfate particles more readily. Substantially all of the available strontium sulfate is converted to strontium carbonate.

The heated mixture of strontium carbonate and sodium sulfate is then gradually cooled. The strontium carbonate settles to the bottom as a crystalline precipitate, While the sodium sulfate liquor gathers as a `top layer. After all of the strontium carbonate crystals have settled out, the sodium sulfate liquor may be Withdrawn, for example by decantation. This liquor may be used as such, or it may be evaporated to dryness in order to collect the sodium sulfate crystals. Both the liquid and solid forms are adapted for certain commercial applications. In this manner a valuable by-product in the manufacture of hydrogen peroxide is obtained.

The strontium carbonate crystals that have been separated from the sodium sulfate liquor are Washed free of sodium sul- Vfio fate. This may be accomplished by washing or leaching the strontium Carbonate particles with Water. After a suitable number of washings to remove any entrained sodium sulfate liquor, 'the crystals or solids of strontium carbonate are preferably filter-pressed and dried. For purposes of'convenience, this strontium 'carbonate product may be referred to es crude strontium carbonate.A

It is next desired to convert the crude strontium carbonate to strontium oxide'. Tn order to ootain this conversion, the crude strontium carbonate, together lwith a suitable carbonaceous reducing agent, such as coal, tar, or the like, is subjected to a smelting or reduction operation. The mixture ofy crude strontium carbonate and carbonaveeous reducing agent may-be subjected' to the reductiony step in the form of a loose, 'ag'- glomerated, or briquetted charge.l The reduction step is preferably conducted with thev use of 12 to 20% by weight of the reducingrr agent, and the mixture is heated to a temperature of about 12000 C. ina suitable reduction chamber, such as a-rotatin-g or Inutile furnace. The charge may be directll orfindirectly heated. The time required varies from six to twelve hours,y depending upon the operating conditions. lf the reduction operation is carefully performed, substantially'allv ofthe available strontium carbonate is reduced tostrontiuml oxide', according to the followingrv reaction:y

v1(2) SrCOi-l-CSrOJqQCO'v The resulting strontium oxide, "which may be referred to as crude strontium oxide, is next leaohed with Water in order to obtain a solution of strontum hydroxidel of convement-strength, say '6% to 10%.- Hydrolysis'of the/"strontium `oxide results when Water' is added thereto, in conformity with the'following'reaction?V K (3) SrO/t H2O?Sr(OH)2` or Sr\ a OH Relativelypure carbon dioxide is then passed into the strontium hydroxide. in order to precipitate out the strontium as strontium carbonate, according to the reaction:

(i) snomnoogesroonnio The carbon dioxide gas'necessary to carbonate the strontium hydroate may conveniently be secured as a by-product in the nreduction operation off the crude strontium to carbon dioxide by burning the same in air.

(5) eoo-'fofeoo2 Moreover, the carbon dioxide gas obtained in this manner may be augmented by the carbon dioxide gas obtained from the heated earbonaceous reducing agent employed in theY reduction operation just mentioned. In otherwvords, some of the carbon in the carbonaceous reducing agent, when subjected to the reduction temperature, is promptly convertedA tocalrbon dioxide gas, quite independent of the reaction taking place between the strontium carbonate and carbon:

Thecombinedcarbondioxide gases are carefully scrubbed, such as lby passing; them through a bodyor spray of Water, in order to remove impurities:

flie strontium carbonate, precipitated in accordancewith equation (t) above, is iiitered from its acconnanying liquor, washed, dried.,l disintegrated Unlike 'the strontium carbonate obtained in the soda ash treatment of tire raw celestite, as shown in equation (l) `above, the preesnt strontium carbon is relatively free of impurities. Substantially all of the objectionable impurities, suoli as iron, silica, alumina and the like, are `eliminated during the vintervening steps. This strontiui'n carbonatemay be referred to as paire strontium carbonate.

t is next; desired to convert the pure strontium carbonate to a substantialiy pure strontium oxideythat may be readily' converted to strontium peroxide.` To this end the pure strontium carbonate is mixed With. a suitable reducingr agent, such as with an equimolecular proportion of ashless carbon. The carbonaceous reducing agent should preferably contain approximately 8.3% of active reducing carbon, so that there may be no unburnt carbon present when all'of the strontium carbonate is reduced to strontium oxide, and so that there may be no, or as little as possible, decomposition of strontium carbonate to strontium oxide by heat alone. When subjected to appropriate reduction temperatures, the heated mixture of strontium carbonate and carbonaceous reducing agente. is converted to strontium oxide and carbonmonoxide, in conformity with the equation sifooi+o=sro+eoo 'lhe reaction represented by this equation is simil-ar to the one indicated in equation (2) above, except that much purer materials enter ir-to the later reaction. |The reduction operation ted must be very carefully conducted in a ciosed multle type furnace of suii'eiently gas tight construction to retain an atmosphere of carbonmonoxide from the Z@as liberated by the reaction in order to ob` lLOO lll.;

tain a final strontium oxide product that may be oxidized to strantium peroxide Without any undue difficulty.

The relatively pure strontium oxide obtained by the last reduction reaction is next converted to relatively pure strontium peroxide. rthis conversion is preferably performed in accordance with the method disclosed in my United `ltates Letters Patent No, 1,325,048. According to the practice of the invention therein (.lisclosed, the strontium oxide is made to react with free oxygen While heated to a temperature of Ll-500o C., and while under about 1300 lbs. pressure per square inch:

ils a result of this oxidizing operation, from 95 to 9( QZ., of the strontium oxide is converted io strontium peroxide. The remainder of the product is largely composed of strontium oxide and strontium carbonate, since extraneous impurities, such as iron, silica, alumina, ete., were, previously eliminated.

'lhe strontium peroxide is next converted into hydrogen peroxide by the use of suitable acids or mixture of acids. In the presrnt preferred practice of the invention, 1 employ a mixture of sulfuric and phosphoric acids. As a result of the reaction precipitates of strontium sulfate and strontium phosphate, and liquid hydrogen peroxide, are formed, accordiiig to the equations:

lu order to obtain a substantially pure hydrogen peroxide free from soluble salts, I have found it advantageous to use a mixture oi' acids cmuprising` about 10% phosphoric and 902/5, sulphuric acids. During the course of the reaction, the reaction mass must be kept relatively cool. The strontium peroxide is first slcked in water to obtain a thin puede of strontiul'n peroxide. This paste is slowly added to the agitated mixture of acids in order to prevent zones of local alkalinity forming in the reaction mass. Such zones of local all-:alinity tend to cause decomposition ot the hydrogen peroxide.

'the alkaline paste of strontium peroxide is added to the acid mixture until the solution is nearly ueutralimul, the temperature of the reaction maus being kept relatively cool. The :itrontiuui sulfate and strontium phixspllatc crystals precipitate out. The liquid portion et the resulting pulp mixture is deeanted from the precipitate, and may be subjected to various treatment processes in order to remove, any impurities. if present, usually by iii-indexing it suliciently alkaline for the purpose. The liquid hydrogen peroxide is then rapidly forced through a filter-press in order lo remove any solids. ythe filtered liquid represents the commercial hydrogen peroxide product.

The strontium sulfate and strontium phosphate precipitates, obtained from the reactions (8) and (9) above, are Washed free of liquid hydrogen peroxide. Due to the relative amounts of acids originally employed, the precipitate will be composed of approximately 90% strontium sulfate and 10% strontium phosphate. The combined precipitates are then treated With an excess of sulfuric acid to remove the acid soluble strontium phosphate, according to the following reaction:

(11) sismo.)2izinzsoi:3srso..+21i.1 o4

The effect of this reaction is to convert the strontium phosphate to strontium sulfate and phosphoric. acid. The excess sulfuric acid. containing the regenerated phosphoric acid, gathers as a top liquor, and may be readily decanted. The strontium sulfate precipitate is Washed several times With Water to remove the sulfuric and phosphoric acids as completely as possible. These Wash liquors are added to the top layer of liquor decanted. Suitable additions of sulfuric acid may be made to this mixture of decanted and Wash liquors in order to treat a new batch of strontium peroxide. The total effect is to reg-enerate the phosphoric acid, which may be used over and over again in the practice of the invention. This is a very desirable economy because ofthe high cost of phosphoric acid. On the other hand, the strontium sulfate recovered in this operation is a valuable byproduct, and may be suitably recovered for commercial usage.

The strontium sulfate obtained by the reaction above is preferably filtered, and employed for the preparation of more strontium peroxide. To this end, it may itself be subjected to the soda ash treatment outlined above, or it may be suitably mixed with celestite about to be subjected to the practice of the invention. Since there is no substantial loss of strontium throughout the Whole process, the strontium sulfate maybe used over and over againtomakehydrogenperoxide. Whatever slight losses of strontium result in the practice of the invention may be made up by suitable additions of relatively small amounts of celestite at the beginning of the process.

If, as is often the case, the Weak hydrogen peroxide is to be concentrated to a 27.0% H2O2 content, a more advantageous procedure is to add just enough strontium peroxide in equations (9) and (10) to selectively react with the sulphuric acid, thereby substantially avoiding reaction With the phosphoric acid. The resulting products then are a precipitate of strontium sulfate, practically uncontaminated vvith strontium phosphate, and top liquor containing hydrogen peroxide and phosphoric acid. The hydrogen peroxide may be completely distilled under high vacuum, say not less thani25v of mercury, from the phosphoric acid. A suitable apparatus for carryingr out the. distillation has been found to be one of glass lined iron.

The products of the distillation then are a distillate of highly pure hydrogen peroxide ot approximately the strength of the original rtop liquor, and the residuo renrainingF in the still is phosphoric` acid. "he weak hydrogen peroxide ma)v now be concentrated to give a 27.0% solution, under vacuum as noted above, except that the distillation is stopped when the hydrogen peroxide in the still reaches QOf/i. About 85% remains as a 27% solution, and about 15% passes over in the distillate. This distillate may berecoinbined with the residual phosphoric acid from the first distillate. hulphuric acid may next be added to the mixture and more weak hydron'en peroxide pregiiared according to equations and (l0) above.

lVhile sulfuric and phosphoric acids hare been indicated as the preterriai acids to be employed in the `practice of the invtution, to obtain a substiniially pure hydrogen peroxide product unwntaminated with soluble salts. other arids. either alone or in conlioint use with other acid or acids. might be employed tor the same purpose. For example, such acids as hydroilnoric. silicotluoric` boreiluoric in substantially the 'ln-o'iortions indicated tor phos horic minht also be eniployed. 0n the other hand. ii the presence ot' soluble strontium salts in the final hydrogen peroxide is not objectionable for certain commercial applications, other acids, such as niurifitic or nitric may be used.

ln case hydrotluoric acid is used. it can be substantially coinililetely recovered by treating the mixture oi strontiui'n sulfato and strontium fluoride with courent rated sulfuric acid and heating. the h vdrolluoric acid beingf thus liberated and volatilized in a"cordance with the following' reaction I (i2) SrSo, 'l' SrR, 't HS() f-r-QSrStl, 'l- QHF and may be recowred bv comlensation; or. the combined precipitates of strontium sulfate and strontium fluoride may be treated with au alkali metal compound. such as concrntratcd sodium carbonate s-tolntion, when the strontium liuoride will be converted to strontium carbonate and sodium fluoride. ac cording' to the tollewiimr reaction:

(i3) Sli-F: -lY NaOP, :1' til-CO; "t QNaF Whichniay` be converted to a substantially water soluble compound such as sodium sulfate, by treating the liquor with an excess of a suitable alkali earth, such as calcium sulfate, when the following reaction will take place:

(14) QNaF -t CaSO4 :I NaSO4 i Call2 The calcium tluoride being insoluble in Water and the calciun'i sulfate being very dilliculty :.uiluble, therefore, both the calcium fluoride and tue excess ialcium sulfate separate out as precipitates, and the clear pure sodium sulfate liquor may be decanted otli.

By treating the precipitated calcium fluoride with concentrated sulfuric acid and heating, the hydroiluoric acid may be recovered and calcium sulfate obtained, both ol' which may be used again.

(15) earn-insofcaso4 i enr lf'iwying the prac ice ot the invention in retrospect, it will be observed that the net result is to ell'tct the manufacture ot' hydrogen peroxide, by thc tixation of oxygen. This resuit is obtained bj.' using strontium oxide as an oxy fen carrier. Soda ash, carbon and sull`nric acid are employed as auxiliary raw materials. th rontium sulfate, phosphoric or hydroiiuoric arids :irc each rcp'enerattul, except Ytor certain mechanical losses that may total trom l() to 20%.

hioreover, certain ialuable byproducts a re also obtai d---more ially sodium sulfate. Carbon monoxide resulting' 'from the reduction operations is converted Yto carbon dioxide, and employed as a carbouatingr agent. Y

Because ot the regeneration of tlu` Very valuable strontium sulfate, whica is substantially pure, and the phosphoric acid. the i vention may be practiced with considerable rconomy. Morciiiver, 'he prom-'ss lends itself particularly well to the manufacture ot a. linal hydrogen peroxide product that is substantially pure.

l claim:

l. The method ot manu lacturing hydrogen peroz'ide which comprises bringing together strontium peroxide and an appropriate mixture ol sulfuric acid and pl'iosphoric acid whereby there are torinod hydrogen peroxide, stroi'itium sulfate and strontium phosphate, separating' the liquid hydrogen peroxide portion 'from the precipitate or" strontium sulfate and strontium phosphate, and converting the strontium phosphate to phosphoric acid and strontium sulfate.

Q. Tl ie method ot manufacturing hydrogen peroxide which compri suitably converting strontium sulfate to relatively pure strontium peroxide, bringing together said strontium peroxide and a mixture oli' sulphuric acid and phosphoric acid While maintaining the reaction mass at a relatively low temperature liti Cfr

to form hydrogen peroxide, strontium sulfate and strontium phosphate, separating the liquid hydrogen peroxide from said strontium salts regenerating phosphoric acid from said strontium phosphate by means of sulfuric acid, and employing the strontium sulfate so recovered for the formation of more strontium peroxide.

3. The method of manufacturing hydrogen peroxide which comprises, treating strontium sulphate with soluble carbonate to form strontium carbonate, converting the strontium carbonate to strontium oxide, oxidizing the strontium oxide to strontium peroxide, treating the strontium peroxide With sulphuric acid to form hydrogen peroxide and strontium sulphate, separating the strontium sulphate from the hydrogen peroxide and returning the strontium sulphate to the process.

4. A process according to claim 3, in which the sulfuric acid solution contains a small amount of phosphoric acid.

5. A process according to claim 3, in which the strontium carbonate is converted to crude strontium oxide, leaching the crude oxide with water to obtain pure strontium hydroxide, and then converting the strontium hydroxide to strontium oxide.

6. A process according to claim 3, in Which the strontium carbonate is heated in the presence of a carbonaceous reducing agent to form crude strontium oxide and carbon monoxide, oxidizing the carbon monoxide to carbon dioxide, leaching the crude strontium oxide With Water to form strontium hydroxide, 

